difference between inert and adiabatic surface

[luca.mi...@gmail.com]

Hi all,

I am a new FDS user, sorry for the simple question, I read the Fire Dynamics Simulator User’s Guide, but I did not understand  which is the difference between inert surface and adiabatic surface.

Sorry again and thank you.

Luca

[dr_jfloyd]

Inert is a wall with the temperature fixed to ambient. Adiabatic is a wall with no net heat transfer.

[Salah Benkorichi]

Check this work to understand about AST 

http://ws680.nist.gov/publication/get_pdf.cfm?pub_id=900083

On 5 June 2017 at 15:03, dr_jfloyd <drjf...@gmail.com> wrote:

Inert is a wall with the temperature fixed to ambient. Adiabatic is a wall with no net heat transfer.

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[Ben Ralph]

If you are not from a heat transfer background - I would recommend not jumping straight in to reading about adiabatic surface temperature as the theory, naming, application may confuse you.

To understand what an adiabatic boundary condition is; instead read some heat transfer/thermodynamics basics (Wikipedia is as good a place to start as any and you can get references there; or go straight for a book like Cengel and Boles "Thermodynamics, an engineering approach").

In short - adiabatic means no net heat transfer between wall and gas.

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[luca.mi...@gmail.com]

Thank you for the answers. I have studied on Cengel at university (I love that book), I will check for the definition of inert surface. It was clear to me the meaning of adiabatic, but not the meaning of inert. 

I have seen on the web that a lot of people uses inert surfaces in order to model the walls and ceilings of the enclosures , so I was wondering when the use of inert surface is the best solution. Does the inert surface have a net heat transfer between wall and gas?

Il giorno lunedì 5 giugno 2017 16:29:27 UTC+2, Ben Ralph ha scritto:

If you are not from a heat transfer background - I would recommend not jumping straight in to reading about adiabatic surface temperature as the theory, naming, application may confuse you.

To understand what an adiabatic boundary condition is; instead read some heat transfer/thermodynamics basics (Wikipedia is as good a place to start as any and you can get references there; or go straight for a book like Cengel and Boles "Thermodynamics, an engineering approach").

In short - adiabatic means no net heat transfer between wall and gas.

On 5 June 2017 at 15:12, Salah Benkorichi <benkori...@gmail.com> wrote:

Check this work to understand about AST 

http://ws680.nist.gov/publication/get_pdf.cfm?pub_id=900083

On 5 June 2017 at 15:03, dr_jfloyd <drjf...@gmail.com> wrote:

Inert is a wall with the temperature fixed to ambient. Adiabatic is a wall with no net heat transfer.

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[dr_jfloyd]

The inert surface always equals the initial ambient temperature. In my opinion it is almost never the best surface for typical building materials in a fire environment. Since it is always ambient, if it sees the fire or hot gasses (either directly or via radiation) then there will be net heat transfer to the surface.

[luca.mi...@gmail.com]

Ok thank you very much. 

So if my aim is to evaluate the structural behavior in order to find a temperature-time curve, maybe I can use adiabatic surfaces with AST devices. If I want to evaluate the visibility in the building, maybe the inert surface can be used since the smoke is going to fall earlier because it gets cold earlier. Isn't it?

Thanks in advance

[dr_jfloyd]

The solid phase 1D heat transfer model costs very little in terms of computational time.  I would recommend defining material properties for your surfaces rather than introducing error by assuming a fictitious thermal boundary condition.